The present invention relates to a ferromagnetic metal powder suitable as a constitutional material for the magnetic layer of magnetic recording media such as magnetic tapes and disks.
As a result of the increase in recording density, magnetic recording media such as magnetic tapes and disks for use in audio, video and computer technologies have become increasingly smaller in size and better in performance and the magnetic powders for such recording media are accordingly shifting from the conventional iron oxide systems to metallic magnetic powders having higher coercive force and saturation magnetization.
The metallic magnetic powders for use in high-density magnetic recording applications are based typically on iron but sometimes on metals such as Ni and Co.
The common industrial process for the manufacture of iron base magnetic powders starts with iron oxyhydroxide or iron oxide-based acicular particles and consists of having an anti-sintering agent such as Si, Al, Zr or Ca deposited or adsorbed on the needles and thereafter reducing them with heat.
When synthesizing iron oxyhydroxide- or iron oxide-based compounds on an industrial scale, compounds of elements of Group Ia of the periodic table such as NaOH, Na.sub.2 CO.sub.3 and KOH have been used as neutralizing agents for the principal reasons of low price and ease in handling. This has eventually produced metallic magnetic powders in which elements of Group Ia of the periodic table such as Na and K more or less remain as incidental impurities on the surfaces of the particles.
This is also true with elements of Group IIa of the periodic table. As taught in Examined Japanese Patent Publication (kokoku) Sho 59-32882 and Unexamined Published Japanese Patent Application (kokai) Hei 2-107701, those elements are occasionally used as anti-sintering agents or the like, which eventually remain on the metallic magnetic powders produced.